PNG backround picture not transparent for some users

Hi community,

I'm having kind of strange issue, where some users are reporting a non-transparent background while using a PNG image.

They choose the same file as everyone else, where it is working perfectly fine (just the company logos are shown), and it just gets shown like a regular JPG image white a grey background, even though there is no background configured in the PNG file. There isn't even another file to choose from, it's only the PNG.
It's even stranger, because two new employees started at the same time, with similar devices on the same patch level and Teams version, even BIOS and drivers are the same, similar webcams and they have different results.

I've checked the following:

- The users have similar settings, no green screen settings turned on, reseted local settings, same result
- We have exchanged files, downloaded the user's background picture, where it's not working, put them in some random users Teams background, boom -> it's working fine

- Maybe some kind of webcam incompatibility, but it even works with some random non-name-brand webcams lying around. Both users used the built-in webcam

- Turned off hardware acceleration in Edge, some blog entry told me that's also a settings for Teams.

- tried different resolutions on therer monitors, same result

I'm still not fully convinced that it's not some kind of PNG file issue, even though our designer reassured me, that it's not the case.

Do you have any ideas, what's my issue here? Am i missing some setting?